The SEM in the Department of Geological Sciences combines an analog (photographic film) and a digital imaging system for recording electron, and, in the not to distant future, electron diffraction and cathodoluminescence images plus we recently installed an x-ray element analysis detector. These instructions are intended to guide the user in acquiring high quality SEM and BSE images by way of optimal electron beam and detector operations. Other instruction sets will be developed to aid fancy detector operations.
The three main units core to the SEM are the column, the control and display system and the power supply. Attached to these units are a vacuum pump, a vacuum control box and an Intel 486DX clone running DOS. Utilities supporting the SEM are a Haskris water recirculating chiller, 220 VAC power and two sources of gas, a bottle of dry nitrogen and compressed air from the Woodhouse Lab building supply.
Operation of the SEM is carried out via mostly digital controls although some look and behave like analog devices. On the column are stage controls and switches used operate an airlock. This airlock that allows the exchange of specimens without leaking the high vacuum in the electron beam column. On the control and display system is a three monitor display panel. On the counter of the control and display system is a 1st control panel that looks like a computer key pad except it is decorated with knobs and square switches, a track ball mouse-like device and two conventional computer keyboards. There is a 2nd control panel on a long strip below the monitors. There is small a power supply control panel with a key and a room light switch below on the right. The JEOL computer keyboard is connected directly to the SEM and can be used to operate without Intel computer. The other is the Intel keyboard.
Specimen preparation:
Specimen preparation commonly includes desiccation and gold-palladium coating. See references at the end for guidelines. Alternatively, geological specimens commonly can be carbon coated if BSE imaging or x-ray analysis are the intended modes. Frequently specimens can be attached to 12.5 or 10 mm diameter metal stubs or Cambridge type pin mounts preferably using double stick carbon tape. Silver and carbon paints tend to flake and do not provide a very strong sticking properties.
Specimen Exchange:
Always use forceps or gloves to handle specimens and specimen holders to avoid contamination of the vacuum system with skin oils. Two main specimen holders are used with the airlock. Specimen holder A can accept stub and pin type mounts with suitable adapters stored in the gray desk, top right. Specimen holder B is designed for 1 inch diameter slides, 1 1/4 inch diameter slides and can support standard petrographic thinsections using carbon conductive tape. Mount the specimen in the appropriate holder, using the microscope if necessary. Measure the height of your specimen above the specimen holder rim in mm. This height must be known to set a correct working distance (WD). Place the sample holder near the edge of the desk for attachment to the specimen exchange rod.
Specimen Exchange procedure:
1. Slowly turn down filament emission (right end of control panel 2).
2. Step down accelerating voltage to 13 kv with ACCEL VOLTAGE knob (right of center on control panel 2).
3. Switch off ACCEL VOLTAGE with switch next to the knob.
4. Set WD to 39 mm using the large gray knob on the top of the stage. A red light on the face of the airlock box is bright if the stage is in the correct 39 mm WD.
5. Center the stage at 25 mm X axis position. If the computer is off, use the silver knob on the stage motor bottom, center. Read the position value near the the stage face.
6. Remove white plastic plug from specimen exchange airlock and place on the column counter.
7. Locate specimen exchange rod stored under plastic box. Avoid touching the rod, which is covered with vacuum grease, by holding by the red knob and the Perspex disk.
8. Screw specimen exchange rod to sample holder with the mounted specimen. Use a gloved hand or heavy object to support specimen holder.
9. Slide Perspex disk to the specimen end of the rod far enough that clips will attach to the specimen holder end of the rod.
10. Hold the Perspex disk up against the o-ring of the airlock.
11. Press the lighted red button on the top of the airlock valve housing just to the right of the airlock. Vacuum will hold the disk and specimen holder very soon. You can now allow the vacuum to support the specimen and rod until step 17.
12. When the red light in step 11 goes out, open the airlock door by rotating the gray knob on the right side of airlock top toward you and then slide it out to the tight until it stops.
13. If the light inside the SEM goes on you have remembered to follow steps 1 through 5.
14. Slide the sample exchange rod in to mount the specimen holder onto a dove tail fixture on the top of the stage. Bifocals make this tough.
15. Withdraw the sample exchanges rod so that it clips to the fixture on the Perspex disk.
16. Close the airlock door securely and rotate the gray knob, your side up, so that the label "open->" is facing upwards.
17. Be prepared to catch the specimen exchange rod as it will fall as soon as the airlock comes to atmospheric pressure. Press the now extinguished red button on the right top of the stage.
18. Return the specimen exchange rod to it's plastic home and replace the white plastic cap over the airlock port.
19. When the vacuum is adequate (see section 4 below),turn on the ACCEL VOLTAGE, step up to your accelerating voltage to the working value, commonly 15 kv, and re-saturate the filament (see section 3 below).
20. Adjust the large gray WD knob to a position appropriate for your specimen height and working conditions. ie: A sample that is 3mm tall can be positioned to the 8 mm WD and have 5 mm clearance for high resolution SEM observations, 15 mm would be appropriate if high resolution BSE observations are needed.
Setting up the electron beam column:
The left monitor is a CRT that displays the real time, analog SEM or BSE image as it is acquired. The function is much like an old radar screen. The image can be scanned at TV rates where there is a rapid change as you, for example, move or re-focus the image. This same left CRT can display a slow scan, where it takes 2 or 10 seconds or longer to collect an image, by relying on a slow decay of the image above the moving scan line. The scan shows the specimen instantaneously as the beam scans.
The middle monitor is a digital CRT that displays the contents of RAM on a computer digital image board located inside the main console. Various functions are available to average many scans, commonly 64, or a single scan. Typical operations will automatically select an appropriate mode for the middle CRT. The microscopist will usually watch the left CRT for focusing, navigation and framing while the middle CRT has a clearer image best for interpreting details of the specimen.
The right monitor is a true computer monitor dedicated to the Intel 486DX. Although image processing software is available on the Intel, this monitor is mostly used to control SEM functions and the stage.
Starting the SEM:
1. Switch on the right monitor using the rocker switch below the right corner. Adjust the middle and left CRTs for brightness and contrast using the thumb knobs blow their lower right corners. Black lines drawn on the front surfaces of the knobs offer a guide for best settings.
2. On the right monitor locate the JEOL Vision Control Console. The COLUMN screen displays controls for the electron beam column. Most of these controls are duplicated on the 1st and 2nd control panels, but you can observe the values of each setting dynamically as you manipulate knob controls. It is also possible to track ball click on value entries and change them with the computer key pad.
3. Check the WD entry, 7th down on the left, and make sure the value corresponds to the position of the large gray knob on the stage. Change the value if it is not correct.
4. On the JEOL keyboard use BREAK and ESC to bring up the operating condition displays. BREAK switches this display on and off while ESC changes control between the CRTs.
5. On the 2nd control panel locate the ACC VOLTAGE square button and knob. Turn the knob until the displays show 13 KV. Push the ACC VOLTAGE button which will light up. Turn the knob CW for the appropriate accelerating voltage, commonly 15 KV.
6. On the 1st control panel in the SW IMAGE section, turn BRIGHTNESS until the left CRT is just gray.
7. In the SCAN section of the 1st control panel switch MODE, which will light, until a line is obtained on the left CRT. If a cross is observed, switch MODE again.
8. Locate the EMISSION (CURRENT/FILAMENT) switch and knob at the right end of the 2nd control panel. Observing the line, turn the EMISSION knob past the first rise in line position to a plateau in line position. If the line goes to the top of the CRT, bring it back to the middle with BRIGHTNESS.
9. Locate GUN ALIGNMENT between ACCEL VOLTAGE and EMISSION. The SHIFT button should not be lighted. Adjust alternately the X and Y knobs for highest vertical position of the left CRT line.
10. Adjust the EMISSION knob to re-locate the maximum position of the line.
11. Repeat 9 and 10 if there is a noticeable improvement in the vertical line position.
12. Set the line about 2 mm below maximum.
Imaging and the 1 st control panel:
1. Switch PIC in the SCAN section.
2. Adjust CONTRAST and BRIGHTNESS right end.
3. Adjust the scan speed to TV using the FAST switch. Two speeds are available, 60 Hz and 30 Hz. 30 Hz flickers a bit. Below about 80 X the 60 Hz rate is not available.
4. MAGNIFICATION on 1 st control panel can be adjusted. INST will give 100 X instantaneously.
5. FOCUS can be coarse or FINE by pressing the switch next to FOCUS. Typically it is necessary to make large, rapid sweeping motions to be able to observe focus properly.
6. PROBE CURRENT adjusts the beam diameter which is the spot size and beam current. Each increases counterclockwise because this control direction decreases current to the condenser lenses producing less squeeze on the beam.
7. SHIFT with X and Y knobs can make fine adjustments to the sample view position when the POSN switch is not lighted.
8. STIGMATOR is used to correct the shape of the electron beam. For example, if the beam shape as it strikes the sample is football shaped with the long axis NW-SE, turn the X control counterclockwise to squeeze it back a circle. Correction of the STIGMATOR can be carried out at high magnification as an improvement in focus. Commonly good values can be entered in the COLUMN menu as recorded on a small sheet of paper under the 1st control panel. STIGMATOR correction is an advanced skill.
9. Under DISPLAY:
a. WFM is the wave form monitor that serves as a light meter. 6 lines appear on the left CRT while an image is collected on the middle CRT. The brightness of the image is shown as the vertical position of a wiggly line on a scale of volts from 0 to 5 volts. Correct BRIGHTNESS to move the wiggly line up and down to fit the scale. Correct CONTRAST to squeeze or expand the range of values of the wiggly line. View the image to see where the measure is being made. For most photography, a good image is produced when all important image elements fall between 0 and 5 volts.
b. D-MAG reduces the size of the image on the left CRT to aid in focusing.
c. FREZ captures a single frame on the digital middle CRT that can be recorded to disk or sent over the computer network to another computer. (See section 7 below)
10. Under PHOTO:
a. ACB will correct contrast and brightness automatically in the SEM (SEI) mode. This does a fair job for a photo, a good starting point for a photo set up. Not useful for BSE images.
b. LEFT will photograph the left CRT to the film camera. 2000 line resolution.
c. RIGHT will photograph the digital image, middle CRT, to the film camera. 1024 line resolution.
To capture a digital image (FIS):
1. Obtain the desired image, focus, adjust sample position to frame up and use scan rotation to obtain the digital image.
2. Label the frame with a combination of letters and numbers that uniquely identifies the image/specimen:
a. Press INS on the Intel computer key board.
b. FLR XXXXXX where Xs are your 6 character frame label. (ie: UCSB34)
Note the frame label in your records for later identification.
c. Enter.
3. WFM under DISPLAY on the 1 st control panel. The 5 lines represent 0 to 5 volts where 0 represents black and 5 represents white. The middle CRT will scan slowly while the left CRT displays a wiggly line showing the brightness of the image at each part of the image. Adjust BRIGHTNESS and CONTRAST so that all image elements are within the 0 to 5 range. Sometimes there are minor image elements, such as a crack, that will go below black. Similarly, there may be vertical edges or small bits of crud that go above white. Images with more than a few percent below black or above white are usually a waste of disk space. Press WFM to turn off the wave form monitor.
4. Press the SCAN button with the track ball on the computer control monitor.
5. Be sure the FREZ button under DISPLAY is dim. Under SCAN SPEED select the second 80 second scan speed to obtain the 1000 line/frame resolution. The image should begin acquisition immediately.
6. When the image is complete, press FREZ under DISPLAY to capture the image to memory. A prompt "FREZ Working" will appear.
7. Press the IMAGING icon on the top left of the control menu.
8. Press the RECEIVE icon on the top left of the control menu. The image should transfer to computer memory. TRANSFERING DIGITAL IMAGE FROM FIS should be displayed as the transfer occurs.
9. A form will appear that you can use to record image data that is spreadsheet compatible. Enter at least an IMAGE TITLE, enter, enter and CLOSE.
10. Press the OPTICAL icon third from the bottom. Click SAVE TO DISK.
11. The PATH should be \IMAGES\. For FILE: user a maximum of 8 characters with no punctuation as the file name and record this in your notes and enter. Click OKAY. The prompt SAVING DIGITAL IMAGE TO OPTICAL DISK should display.
12. Click the CONTROL icon on the bottom to return to the standard control screen. Click the COLUMN button to return to the standard selection.
To FTP a file:
1. Exit from the JEOL control program on the Intel monitor.
2. Ctrl-Alt-Del to re-start the Intel.
3. Select 4. NET_DOS from the menu.
4. e:
5. cd images Here you can dir to see your stored file on the list for the disk drive.
6. ftp magic.geol.ucsb.edu and give Name: as anonymous and Password: your name
7. binary
8. cd /pub/chert
9. send filename.tif
10. quit
11. Ctrl-Alt-Del
12. At the prompt select 2. Vision. The normal command display will initialize.
Photography:
1. Obtain the desired image, focus, adjust sample position to frame up and use scan rotation to obtain the image for a photograph. Set scan SPEED to FAST.
2. Label the frame with a combination of letters and numbers that uniquely identifies the image/specimen:
a. Press INS on the Intel computer key board.
b. FLL XXXXXX where Xs are your 6 character frame label. (ie: UCSB35)
Note the frame label in your records for later identification. Subsequent images will increment the label if it ends in a numeric character.
c. Enter.
2. WFM under DISPLAY on the 1 st control panel. The 5 lines represent 0 to 5 volts where 0 represents black and 5 represents white. The middle CRT will scan slowly while the left CRT displays a wiggly line showing the brightness of the image at each part of the image. Adjust BRIGHTNESS and CONTRAST so that all image elements are within the 0 to 5 range. Sometimes there are minor image elements, such as a crack, that will go below black. Similarly, there may be vertical edges or small bits of crud that go above white. Images with more than a few percent below black or above white are usually a waste of film. Press WFM to turn off the wave form monitor.
3. Turn the magnification up X 10 to make a final check on focus and back to the magnification for the photograph.
4. Slide film into the camera and/or open the dark slide on the camera.
5. Verify that the PHOTO scan speed is the first 80 which represents 80 seconds to collect the image with a line resolution with about 2000 lines/frame. Click the SCAN button on the computer display. Under PHOTO SPEED note that the speeds available are 40, 80, 80, 160, and 320. The first 80 is correct. Click COLUMN.
6. Under PHOTO press LEFT. (RIGHT will photograph the digital image on the middle CRT.) Wait while the 80 second scan is generated ... don't bump the column.
7. When complete, slide in the dark slide on the camera, flip the processing lever and/or smoothly and in one clean not-too-fast motion, pull out the photo. Obviously roll film will only require complete (1 1/2 strokes!) film advance.
8. Process film for 25 or 30 seconds as indicated on the film instructions. Tear print away from negative in one clean, even motion. Process negative and coat print.
Imaging with backscattered electrons (BSE):
The BSE detector is located (currently) on the right side of the column. It comprises a black cylinder labeled "Robinson Detector" mounted on two thin rods and a thicker tube. The business end inside the vacuum is about 5 mm thick, so you need to be sure there is room above your sample for the BSE detector to pass between sample and electron column. A working distance of at least 15 mm should be used.
The control box for the BSE is located in the accessory cabinet hanging off of the extreme right end of the SEM console. Locate brightness, contrast and a power switch.
1. A knurled screw on top at an angle locks the detector in a withdrawn position. Loosen this screw and gently slide the detector in until it stops. Sometimes the lower rod needs to be encouraged back into its guide hole as you wiggle the body for he detector.
2. Power on.
3. On the 2 nd control panel under IMAGE SELECTOR press AUX.
4. Beam current should be relatively high, CL COARSE at 6 and CL FINE at 0. Adjust PROBE CURRENT, BSE brightness and BSE contrast to taste. CL FINE can only be changed by clicking and entering a value. (hint: It seems to be helpful to enter a value of 100 for CL FINE, adjusting CL COARSE to about 4. Then enter values in CL FINE until the image is perfect. Don't forget, a higher CL number is lower beam current.)
5. Obtain the desired image, focus, adjust sample position to frame up and use scan rotation to obtain the image.
6. Follow instructions for photography or digital capture.
7. When finished, withdraw the BSE detector and lock. Switch IMAGE SELECTOR to SEI for secondary electron imaging in the SEM mode.
Shut down at the end of the day:
1. On the JEOL computer keyboard press BREAK to turn off the alphanumeric data that makes up the basic screen display at the bottom of the middle CRT. An underline prompt will appear at the upper left.
2. Press ESC on the JEOL keyboard to transfer control to the left CRT.
3. Press BREAK to turn off the left screen basic display data.
4. Turn down brightness to black.
5. Turn down the CONTRAST and BRIGHTNESS on both CRTs.
6. Switch off the Intel monitor with the rocker switch below the display.